Which one of the following is NOT found in a prokaryotic cell ?
- A.Cell wall
- B.Ribosome
- C.Nuclear membrane
- D.Plasmid DNA
Correct answer
Explanation
The correct answer is C, Nuclear membrane. A prokaryotic cell has no true nucleus, so its genetic material is not wrapped in a nuclear membrane.
Bacteria and cyanobacteria are prokaryotes. Their single circular chromosome lies naked in a region of the cytoplasm called the nucleoid. They also lack membrane-bound organelles such as mitochondria, chloroplasts, the Golgi body and the endoplasmic reticulum. Eukaryotic cells of plants, animals and fungi, by contrast, have a nucleus enclosed by a double nuclear envelope with pores.
Option A is wrong because most prokaryotes have a rigid cell wall, made of peptidoglycan in bacteria. Option B is wrong because prokaryotes do have ribosomes, the smaller 70S type, to make proteins. Option D is wrong because many bacteria carry plasmids, small extra rings of DNA that often hold genes for antibiotic resistance and are used as vectors in genetic engineering.
Exam tip: prokaryote = nucleoid, 70S ribosomes, no nuclear membrane; eukaryote = true nucleus, 80S ribosomes.
Practice Questions
View allThe fact that the planets move around the Sun, not in circles but in ellipses, was first demonstrated by
- A.Galileo
- B.Martin Luther
- C.Johannes Kepler
- D.Copernicus
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In 1609 Kepler showed that the planets move around the Sun in elliptical orbits, with the Sun at one focus of the ellipse.
Read the full explanation →Which one of the following statements is correct?
- A.Urea is produced in liver.
- B.Urea is produced in blood.
- C.Urea is produced from digestion of starch.
- D.Urea is produced in lung and kidney.
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Liver cells turn the toxic ammonia released from the breakdown of amino acids into urea through the ornithine cycle, also called the urea cycle.
Read the full explanation →Which one of the following is the correct sequence of passage of light in a compound microscope?
- A.Condenser-Objective lens-Eyepiece-Body tube
- B.Objective lens-Condenser-Body tube-Eyepiece
- C.Condenser-Objective lens-Body tube-Eyepiece
- D.Eyepiece-Objective lens-Body tube-Mirror
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Light passes through the condenser to the specimen, is picked up by the objective lens, travels up the body tube and reaches the eye through the eyepiece.
Read the full explanation →Which one of the following statements regarding haemoglobin is correct?
- A.Haemoglobin present in RBC can carry only oxygen but not carbon dioxide.
- B.Haemoglobin of RBC can carry both oxygen and carbon dioxide.
- C.Haemoglobin of RBC can carry only carbon dioxide.
- D.Haemoglobin is only used for blood clotting and not for carrying gases.
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It binds oxygen at its iron-containing haem groups and carries some carbon dioxide on its protein chains. Each haemoglobin molecule has four polypeptide chains and four haem groups, and each haem iron can hold one oxygen molecule, forming oxyhaemoglobin in the lungs.
Read the full explanation →Which one of the following statements regarding histone proteins is correct?
- A.Histones are proteins that are present in mitochondrial membrane.
- B.Histones are proteins that are present in nucleus in association with DNA.
- C.Histones are proteins associated with lipids in the cytosol.
- D.Histones are proteins associated with carbohydrates in the cytosol.
Show answer
They are the proteins around which DNA winds to form chromatin in the nucleus of eukaryotic cells. Histones are small basic proteins, rich in the positively charged amino acids lysine and arginine, which attract the negatively charged phosphate groups of DNA.
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